The present invention pertains to apparatus and methods for performing collision resolution for digital control channels and, in particular, to apparatus and methods for performing collision resolution between clashing signals on reverse digital control channels.
The Digital Control Channel (DCCH) was developed to enhance the capabilities of IS-136 (time division multiple access (xe2x80x9cTDMAxe2x80x9d)) cellular systems.
These enhancements included the potential increase in the control channel""s data capacity, improved capabilities related to the mobile station sleep mode for saving battery life and improved capabilities related to short messages services. The logical DCCH structure is composed of a forward channel and a reverse channel. The major functions of the forward link (FDCCH) include broadcasting and access control for mobile users. The reverse link (RDCCH) is dedicated to mobile random access capabilities and functions.
Typically, mobile slot collisions and problems related thereto may occur when multiple users attempt to access the same TDMA slot. Specifically, when two or more users, having comparable signal levels of typically less than a 6 dB power separation, attempt to simultaneously access the reverse link in the IS-136 TDMA system, the receiver at the base station usually fails to detect the signals from any of the users. The base station will then typically request that all of the users re-send their messages after a random time delay.
Although techniques are known which address signal detection in a fading environment, these techniques do not improve system throughput by canceling the co-channel interference in the absence of a reference signal. In conventional systems, a unique word (Coded Digital Verification Color Code (CDVCC word)) in each TDMA slot may be used as a training sequence in order to cancel the co-channel users. However, since all contending users of the RDCCH have identical SYNC words, and no unique CDVCC word, these techniques may not be utilized for improving system throughput.
The DCCH TDMA slot structure is based on the IS-136 digital traffic channel frame. The following is a brief description of how RDCCH handshaking protocol works. When the control channel is utilized by the base station (i.e., the base station is transmitting on the FDCCH), the base station will broadcast continuously to all of the mobiles in that cell. For example, if a mobile desires to transmit on a particular slot, it detects whether that slot is being utilized (i.e. it detects if the base station set a flag bit in the slot). If the flag is not set the mobile will attempt to transmit on that slot and will query the base station as to whether the slot is available.
Once the base station receives and processes this message, the base station sends a reply message, at the next available slot, to the mobile, indicating that a call has been set up. However, the call will not be setup if the base station cannot detect the signal which is sent by the mobile. This failure to detect the signal sent by the mobile could occur if another mobile, transmitting at a similar power level, such as a signal power level within 6 dB of the other mobile""s. signal, attempts to access the slot at the same time. This simultaneous transmission results in a slot collision and a subsequent corruption of the received data. If a clash should occur, with the base station failing to acknowledge that the slot has been allocated, each of the clashing mobiles will typically delay their respective operation for a random time period before attempting to acquire the slot again.
The failure of prior art systems to resolve collisions between mobile units, and thus requiring a retransmission, results in inefficient use of network capacity and decreased throughput.
Accordingly, it is an object of the present invention to provide apparatus and methods for performing collision resolution in communications networks.
It is another object of the present invention to provide apparatus and methods for performing collision resolution on digital control channels.
It is still another object of the present invention to provide apparatus and methods for performing collision resolution between clashing signals on a reverse digital control channel.
It is yet another object of the present invention to provide apparatus and methods for performing collision resolution utilizing blind channel estimates in communication networks and/or on digital control channels.
It is another object of the present invention to provide apparatus and methods for performing collision resolution in communication networks which provides increased network throughput.
It is another object of the present invention to provide apparatus and methods for performing collision resolution in a communication network by utilizing multiple blind channel estimates in a cascaded fashion.
It is yet another object of the present invention to provide apparatus and methods for resolving clashes between signals from users of multiple mobile units who attempt to access the same time slot on the same channel.
It is yet another object of the present invention to provide apparatus and methods for resolving collisions between signals from users of mobile units without having to rely upon the utilization of unique information which corresponds to each of the mobile units.
These and other objects of the invention will become apparent to those skilled in the art from a review of the detailed description of the invention taken in conjunction with the drawings which follow.
In accordance with the teachings of the present invention, these and other objects may be accomplished by the present apparatus and methods for performing collision resolution on interfering signals in digital control channels. An embodiment of the present invention includes at least two antennas, a receiver connected to the antennas and a processor electrically connected to the receiver. The antenna receive interfering signals from mobile stations and provide these signals to the receiver. The receiver may amplify and/or filter the received signals, and/or translate the signals to a baseband frequency. The processor is configured to receive these interfering signals from the receiver, perform a blind channel estimate calculation on each to determine at least one channel parameter thereof and to provide at least one other signal derived at least in part from the channel parameter, to a communication network.
Another embodiment of the invention includes means for receiving interfering signals, means for performing a blind channel estimate calculation on the interfering signals, and means for providing at least one other signal to a communication network. The blind channel estimate is employed to obtain at least one channel parameter of the interfering signals and the signal provided to the communication network is derived at least in part from the channel parameter.
Yet another embodiment of the invention includes a method for performing collision resolution on interfering signals in a digital control channel. The method includes receiving interfering signals on a digital control channel, performing a blind channel estimation calculation on each of the interfering signals to obtain channel information thereof, and using the channel information to obtain a preferred signal.
The invention will next be described in connection with certain exemplary embodiments; however, it should be clear to those skilled in the art that various modifications, additions and subtractions can be made without departing from the spirit or scope of the claims.